Field of the Invention
The present invention relates to a controller, and more particularly, to a controller that performs gap control to keep an amount of gap between a cutting head and a workpiece in controlling a laser machine.
Description of the Related Art
In laser machines, the positional relationship between a cutting head and a workpiece must be held within a predetermined range. To attain this, these machine tools use the technique of gap control such that the distance (amount of gap) between the cutting head and the workpiece is controlled to be kept constant.
When the cutting head passes a place where the workpiece is not present during the gap control, as shown in FIG. 12, it is detected to be located at a height based on a surface further below the workpiece. In some cases, therefore, the gap control may be performed based on the detected height so that the cutting head drops and hits an end of the workpiece, thereby damaging it. In order to prevent such dropping of the cutting head, a technique is proposed in which the height of a cutting head 3 is detected and controlled to be kept within a predetermined range to machine a workpiece 5, as shown in FIG. 13 (e.g., Japanese Patent Application Laid-Open No. 07-112348, hereinafter referred to as the prior art).
However, even if an attempt is made to prevent dropping of the cutting head by applying the above prior art to machining in which the workpiece 5 is inclined as it is machined, as shown in FIG. 14, an area set as a movable range of the cutting head 3 does not change according to this prior art. Thus, in an area (left-side area in FIG. 14) in which a lower limit L of the set movable range of the cutting head 3 is below the surface of the workpiece 5, the cutting head 3 may possibly drop in a place where the workpiece 5 is not present. In an area (right-side area in FIG. 14) in which the lower limit L of the set movable range of the cutting head 3 is above the surface of the workpiece 5, in contrast, the cutting head 3 may not be able to satisfactorily profile the workpiece 5, possibly resulting in defective machining.
Moreover, in machining a pipe as the workpiece, the height of the surface of a workpiece 6 to which beams are applied changes when the workpiece 6 is rotated, as shown in FIG. 15. Therefore, the lower limit L of the movable range of the cutting head 3 never changes even if an attempt is made to prevent dropping of the cutting head 3 by applying the above-described prior art to machining of the workpiece 6. Thus, as in the case of FIG. 14, there is a possibility of the cutting head 3 dropping or failing to satisfactorily profile the workpiece and thereby resulting in defective machining.